


Heir to the Throne

by RayVermilion



Category: Fate/Grand Order
Genre: Anal Sex, F/M, Futanari, Pedophilia, Step-Sibling Incest, Vaginal Sex
Language: English
Status: Completed
Published: 2018-12-24
Updated: 2018-12-24
Packaged: 2019-09-25 09:14:43
Rating: Explicit
Warnings: Rape/Non-Con, Underage
Chapters: 1
Words: 1,245
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17118560
Author URL: https://archiveofourown.org/users/RayVermilion/pseuds/RayVermilion
Summary: Another instance of Merlin's training with Artoria during her days as a young knight. He does what he can to speed up how fast she can mature mentally until the day she becomes King of Britain.





	Heir to the Throne

Artoria Pendragon swung her sword by the river when Merlin called her name. She rushed to his tent, and upon her arrival, he said, “Ready for today’s training?”

“Of course,” Artoria said, nodding. “I’m used to it now.”

“That’s the spirit,” Merlin said, patting Artoria’s head. “But you’ll be practicing something new today.”

“Really? But you said this week would only be sex training.”

“It’s related to that."

“So what’s new this time? Am I supposed to have sex with my brother too?”

Merlin laughed. “Oh it’s nothing like that. If I did that, I’d have to teach him too, but that’s too tedious. Your training is more important than him.” He touched Artoria’s shoulder and she stared at his face, wondering what trick this incubus could be up to this time.

“You see, even though a king can be successful, they’ll be replaced when they die. You’ll need an heir to your throne."

“Then I’ll pick you as my heir,” Artoria said, smiling. “You can definitely do it.”

Merlin chuckled. “I’m flattered, but I refuse.”

Artoria blushed.“How come?”

“The heir has to be related to you.”

"So Sir Kay would take over?"

"Well yes, but he's not fit to be a king. Your heir will be your future child. Remember all the sex we had so far? Kids are made from that.”

Artoria's eyes widened. "That's impossible. We had sex so many times. Shouldn’t one have appeared by now?”

“My magic makes my sperm infertile. I can never make you pregnant.” Merlin gestured towards his tent. “Now come in.”

Artoria crawled inside. As they sat across from each other, she said, “So who'll make me pregnant?

“On the contrary,” Merlin said, smirking. “You’ll make someone pregnant.”

Artoria scratched the back of her head. “But that's impossible."

“Normally yes, but not with my help.” Merlin pressed his hand against Artoria’s stomach. She felt a burning sensation in her abdomen. The pain moved downward to her groin, and she doubled over, clutching her body. It felt like someone kicked her pelvis and then stomped on her genitals. “It—hurts… so much.” She panted as the pain welled up within her hips.

“It’s always like that the first time,” Merlin said, watching Artoria writhe on the tent floor. “Your body’s trying to reject the change, but the pain always stops after the first time.”

Artoria couldn’t believe the pain she was experiencing. She would rather fall off a horse hundred times then go through this. Who could withstand such unbelievable torture? She reached towards Merlin with her right hand, and when she was about to tell him to stop the magic, her body relaxed. She sat upright, smiling at the pain’s disappearance, but then she felt something against her groin. She lifted her skirt and there was the outline of a penis on her underwear. Artoria lowered her underwear and the penis drooped downward like a tree’s branch.

She screamed, "Is this permanent?” but instead of a reply, Merlin grabbed her dick and she clutched onto his arm as she felt the pressure around her penis.

“This is..so much.”

“Time to get used to it,” Merlin said, squeezing Artoria’s penis. “Now you can impregnate someone, but you’ll have to know how to please them. We can’t have rumors about a king that can’t have sex.” Merlin unfastened his pants, dropping them to the ground, and spread his buttocks in front of Artoria.

“Now fuck me.” Merlin said. “Stick it right in.”

Artoria grabbed Merlin’s waist. “Like this?” The tip of her penis pressed against Merlin’s anus, and as it slid deeper within, she hugged Merlin.

“It’s—so tight.”

Merlin moaned. “It’s just right for you. Now give me more.”

With each thrust, Artoria's legs got weaker, but she held onto Merlin as she felt his anus rub against her. The joy of the pleasure excited her, and even though Merlin wanted her to be dominate, Artoria wished her asshole was getting penetrated instead. If Sir Kay was here, she thought, I could see if I was strong enough to take on two men at once.

As the motions continued, Artoria pressed herself against Merlin’s back. “It’s coming out,” she yelled, ejaculating inside of Merlin’s ass. She panted as she held onto Merlin’s hips. Her penis slipped out of his anus, its flaccid appearance made it look pathetic for the dick of a future king. Semen dripped from Merlin’s ass, landing on the tent’s floor. Then he grasped Artoria’s head, pushing her lips against his asshole. “Drink it.”

Artoria scooped out the semen with her tongue. The sperm’s texture reminded her of melted cheese as she swallowed. While Merlin’s semen tasted like orange pulp, her own semen tasted like saltwater.

“Now then,” Merlin said, holding his penis. “Time for you to get some good practice.” He groaned as his dick withdrew into his body, and then a set of ridges formed at his groin. The shapes became more defined, mucus dripped from the surface, and then a clitoris formed.

“You can do that too?” Artoria asked, watching Merlin rub his vagina.

“Of…course,” Merlin replied, in between hushed breaths as he moaned. “Now fuck me.” He spread his vaginal lips with his fingers. “As if I were your future queen.”

When the tip of Artoria’s penis entered Merlin’s vagina, the rest of the shaft penetrated his lubricated womb. She moaned as her dick went in and out of him. Because his vagina was so much more spacious than his asshole, she went into a faster rhythm than before, and the pleasure made Merlin wrap his legs around Artoria. “Right there!” he yelled, gazing at the ceiling. “Keep going.”

“I’m…trying,” Artoria replied. She wondered what else she could do with this penis other than changing speeds. Maybe there was more to this, but if there was than it must be one of those skills that are easy to do, but difficult to master. But since Merlin was enjoying himself, she decided to forgo thinking and just allowed her body to carry herself to pleasure through the warm vagina she was inside of.

Merlin pulled Artoria closer with his legs. “Come on, you’re almost there.”

“This feels better. I think I’m going to cum.”

“Really? Give me all you have. Make me pregnant already.”

“I, I can?”

Merlin winked. “Maybe. If you try hard enough.” 

Heeding his words, Artoria held Merlin’s waist and ejaculated into his vagina. Merlin leaned forward and kissed her cheek. “Not bad for your first time with a dick. I expect better next time though.”

“So, I’m keeping this?” Artoria asked, pointing towards her penis.

“You will when you’re older. For now it’ll only last for a few hours.”

Artoria pouted. “That’s not fair. This feels so much better.”

Merlin patted Artoria’s head. “Your eagerness is good. But you still need more practice with it. Sex is one thing, but you might piss yourself by accident.”

“Watch! I’ll master this like everything else you’ve taught me.”

Despite Merlin’s smirk at these words, Artoria knew this was but another instance of the strange lessons she had to endure with this magus. Even though his methods were unorthodox, she saw the value in the training, and was ready for the day when she would claim Britain’s throne. But until then she’ll cling to her mentor’s instructions, for every surprise he had in store for her would prepare her for the tumultuous battlefields of the future.

**Author's Note:**

> I like this dynamic between Merlin and Artoria and I feel it works when you consider Merlin is part incubus. He would want to have sex all the time right? And if he's busy with training Artoria then he would do both at the same time. Mixing work with pleasure right? This is how I interpret things.


End file.
